Bug fix to ParallelizableJobRunner
Bug fix to ParallelizableJobRunner

The ParallelizableJobRunner would crash intermittently in a multi-core environment during the acquisition of the ProgressMonitor for the next task.  The problem is due to asynchronous access to the LinkedList (a non-thread-safe class) storing these ProgressMonitors.  It has been replaced with a ConcurrentLinkedQueue, which is thread-safe.

bwkimmel/jdcp,bwkimmel/jdcp